1. Field of the Invention
The present invention relates to an image processing apparatus and method that use wavelet transforms to compress images, and to a medium containing a program for implementing the method.
2. Description of the Related Art
Recently, image compression/encoding using wavelet transforms has attracted attention. For example, after an image to be encoded is divided into a plurality of frequency bands (sub-bands) by performing a wavelet transform on the image, transform coefficients in each frequency band are quantized, and the quantized transform coefficients are then entropy-encoded.
One known method for performing a wavelet transform on an original image includes performing horizontal one-dimensional filtering on the original image so as to separate high frequency components and low frequency components, subsequently performing a vertical one-dimensional dimensional filtering on the image, to divide the original image into four sub-bands, LL, LH, HL, and HH, and performing similar processing on LL, which corresponds to low frequency components, to further divide LL into four sub-bands.
The number of times the division of the image should be performed must be optimized depending on the content of the image, etc.
However, conventionally, an optimal method for determining the number of times the sub-band division is performed has not been established.
Accordingly, It is an object of the present invention to perform an efficient wavelet transform to provide sub-bands having a size suitable for being encoded in an encoding unit in a post-stage. In particular, it is an object of the present invention to perform a wavelet transform in which the number of times an original image is divided is optimal.
To these ends, according to an aspect of the present invention, the foregoing objects are achieved through provision of an image processing apparatus including an input unit for inputting an image, a transform unit for performing a two-dimensional discrete wavelet transform on the image to generate a plurality of frequency components, and an entropy encoding unit for performing entropy encoding on each of the frequency components in Mxc3x97N-sized units, where M and N each represent an integer equal to or greater than 1. In a first encoding mode, the transform unit performs the two-dimensional discrete wavelet transform on the image either a predetermined number of times or for a number of times which allows a lowest frequency component to have a size of Mxc3x97N. In a second encoding mode, the transform unit performs the two-dimensional discrete wavelet transform on the image the predetermined number of times.
According to another aspect of the present invention, the foregoing objects are achieved through provision of an image processing apparatus including an input unit for inputting an image, a transform unit for performing a two-dimensional discrete wavelet transform on the image to generate a plurality of frequency components, and an entropy encoding unit for performing entropy encoding on each of the frequency components in Mxc3x97N-sized units, where M and N each represent an integer equal to or greater than 1. The transform unit performs the two-dimensional discrete wavelet transform on the image either a predetermined number of times or for a number of times which allows a lowest frequency component to have a size of Mxc3x97N.
According to another aspect of the present invention, the foregoing objects are achieved through provision of an image processing apparatus including an input unit for inputting an image, a transform unit for performing a two-dimensional discrete wavelet transform on the image to generate a plurality of frequency components, and an entropy encoding unit for performing entropy encoding on each of the frequency components in Mxc3x97N-sized units, where M and N each represent an integer equal to or greater than 1. The transform unit performs the two-dimensional discrete wavelet transform on the image for a number of times which allows a lowest frequency component to have a size of Mxc3x97N.
According to another aspect of the present invention, the foregoing objects are achieved through provision of an image processing apparatus including an input unit for inputting an image, a transform unit for performing a two-dimensional discrete wavelet transform on the image to generate a plurality of frequency components, and an entropy encoding unit for performing entropy encoding on each of the frequency components in Mxc3x97N-sized units, where M and N each represent an integer equal to or greater than 1. In a first encoding mode, the transform unit performs the two-dimensional discrete wavelet transform on the image a predetermined number of times or for a number of times which allows a lowest frequency component to have a predetermined size that is a function of a size of Mxc3x97N, and in a second encoding mode, the transform unit performs the two-dimensional discrete wavelet transform on the image until the predetermined number of times.
According to another aspect of the present invention, the foregoing objects are achieved through provision of an image processing apparatus including an input unit for inputting an image, a transform unit for performing a two-dimensional discrete wavelet transform on the image to generate a plurality of frequency components, and an entropy encoding unit for performing entropy encoding on each of the frequency components in Mxc3x97N-sized units, where M and N each represent an integer equal to or greater than 1. The transform unit performs the two-dimensional discrete wavelet transform on the image until a predetermined number of times or for a number of times which allows a lowest frequency component to have a predetermined size that is a function of a size of Mxc3x97N.
According to another aspect of the present invention, the foregoing objects are achieved through provision of an image processing apparatus including an input unit for inputting an image, a transform unit for performing a two-dimensional discrete wavelet transform on the image to generate a plurality of frequency components, and an entropy encoding unit for performing entropy encoding on each of the frequency components in Mxc3x97N-sized units, where M and N each represent an integer equal to or greater than 1. The transform unit performs the two-dimensional discrete wavelet transform on the image for a number of times which allows a lowest frequency component to have a predetermined size that is a function of a size of Mxc3x97N.
According to a further aspect of the present invention, the foregoing object is achieved through provision of a computer-readable storage medium containing an image processing program including code for performing a transform step for performing a two-dimensional discrete wavelet transform on an input image to generate a plurality of frequency components, and an entropy encoding step for performing entropy encoding, in Mxc3x97N-sized units, on each of the frequency components obtained in the transform step, where M and N each represent an integer equal to or greater than 1. In a first encoding mode, the transform step performs the two-dimensional discrete wavelet transform on the image either a predetermined number of times or for a number of times which allows a lowest frequency component to have a size of Mxc3x97N, and in a second encoding mode, the transform step performs the two-dimensional discrete wavelet transform on the image the predetermined number of times.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.